1. Technical Field
An organic anti-reflective polymer and its preparation method are disclosed. The organic anti-reflective polymer prevents back reflection of lower film layers and eliminates standing waves that are caused by a thickness change the photoresist material and light, in a lithographic process using 248 nm KrF and 193 nm ArF laser light sources for fabricating ultrafine patterns. More particularly, the disclosed organic anti-reflective polymer is useful for fabricating ultrafine patterns of 64M, 256M, 1G, and 4G DRAM semiconductor devices. A composition containing such organic anti-reflective polymer, an anti-reflective coating layer made therefrom and a preparation method thereof are also disclosed.
2. Description of the Background Art
In a fabrication process of ultrafine patterns for preparing semiconductor devices, standing waves and reflective notching inevitably occur due to the optical properties of lower film layer on the wafer and due to thickness changes of photosensitive film. In addition, there is another problem associated with the CD (critical dimension) alteration caused by diffracted and reflected light from the lower film layers. Thus, it has been suggested to introduce anti-reflective coating that enables preventing back reflection at a lower film layer by introducing organic material showing high absorbance at a wavelength range of the light employed as a light source.
Anti-reflective coatings are classified into inorganic and organic anti-reflective coating depending upon the material used, or into absorptive and interfering anti-reflective coating based on the operation mechanism. For microlithography using I-line (365 nm wavelength) radiation, inorganic anti-reflective coatings are predominantly used, while TiN and amorphous carbon as use as an absorptive system and SiON is used as an interfering system.
In a fabrication process of ultrafine patterns using KrF laser, SiON has been mainly used as an inorganic anti-reflective film. However, in the case of an inorganic anti-reflective film, no material has been known which enables the control of the interference at 193 nm, the wavelength of light source. Thus, there has been great deal of efforts to employ an organic compound as an anti-reflective coating.
To be a good organic anti-reflective coating, the following conditions must be satisfied. First, peeling of the photoresist layer due to the dissolution in a solvent must not take place when conducting a lithographic process. In order to achieve this goal, a molded coating must be designed to form a cross-linked structure without producing any chemical as a by-product. Second, chemicals such as acid or amine must not come-in or go-out from the anti-reflective coating. This is because when acid migrates from anti-reflective coating, undercutting occurs at a lower part of the pattern while footing may occur when a base such as amine migrates. Third, the etching speed of the anti-reflective coating should be faster than that of the upper photosensitive film so as to facilitate etching process by using photosensitive film as a mask. Finally, as a result, the anti-reflective coating must be as thin as possible to an extent to sufficiently play a role as an anti-reflective coating.
The existing organic anti-reflective material is mainly divided into two types: (1) polymers containing chromophore, cross-linking agent (single molecule) cross-linking the polymers and an additive (thermally variable oxidant); and (2) polymers which can cross link by themselves and contain chromophore and an additive (thermally variable oxidant). But these two types of anti-reflective material have a problem in that the control of the k value is almost impossible because the content of the chromophore is defined according to the ratio as originally designed at the time of polymerization. Thus, if it is desired to change the k value, it must be synthesized again.
A novel organic polymer for anti-reflective coating and its preparation method are disclosed.
An anti-reflective coating composition comprising the aforementioned polymer and a preparation method thereof are also disclosed.
A semiconductor device on which a pattern is formed from such an anti-reflective coating by submicrolithography is also disclosed.
The following compounds having Formulas 1 and 2, respectively are provided which can be used in an anti-reflective coating. 
In the above Formulas 1 and 2:
Ra to Rd are each independently hydrogen or methyl;
Ra to Rd, and R1 to R18 are each independently xe2x80x94H, xe2x80x94OH, xe2x80x94OCOCH3, xe2x80x94COOH, xe2x80x94CH2OH, or substituted or unsubstituted, or straight or branched alkyl or alkoxy alkyl having 1 to 5 carbon atoms;
1, m and n each represents an integer selected from 1, 2, 3, 4 and 5;
w, x, y, and z each represents mole fraction from 0.01 to 0.99;
R19 and R20 are each independently straight or branched substituted C1-10 alkoxy; and
R21 is hydrogen or methyl.
The compound of Formula 2 is prepared by polymerizing (meth)acrolein to obtain poly(meth)acrolein followed by reacting the obtained polymeric product with branched or straight substituted alkyl alcohol having 1 to 10 carbon atoms.
In detail, (meth)acrolein is first dissolved in an organic solvent and added thereto a polymerization initiator to carry out polymerization under a vacuum at a temperature ranging from about 60 to about 70xc2x0 C. for a time period ranging from about 4 to about 6 hours. Then, the obtained polymeric product is reacted with branched or straight substituted alkyl alcohol having 1 to 10 carbon atoms in the presence of trifluoromethylsulfonic acid as a catalyst at a room temperature for 20 to 30 hours.
In the above process, suitable organic solvent is selected from the group consisting of tetrahydrofuran (THF), cyclohexanone, dimethylformamide, dimethylsulfoxide, dioxane, methylethylketone, benzene, toluene, xylene and mixtures thereof. As a polymerization initiator, it can be mentioned 2,2-azobisisobutyronitrile (AIBN), benzoylperoxide, acetylperoxide, laurylperoxide, t-butylperacetate, t-butylhydroperoxide or di-t-butylperoxide. A preferred example of the said alkyl alcohol having 1 to 10 carbon atoms is ethanol or methanol.
A preferred compound of Formula 2 is selected from the group consisting of the compounds of the following Formulas 3 to 6. 
The above compounds of Formulas 3 to 6 are readily cured in the presence of acid and other polymers having alcohol group.
The polymer of Formula 1 is prepared by reacting 9-anthracene methyliminealkylacrylate monomer, hydroxyalkylacrylate monomer, glycidylalkylacrylate monomer and 9-anthracenealkylmethacrylate in an organic solvent and then polymerizing the obtained compound with a polymerization initiator. Any conventional organic solvent can be used in this process but a preferred solvent is selected from the group consisting of tetrahydrofluran, toluene, benzene, methylethylketone, dioxane and mixtures thereof. As a polymerization initiator, any conventional radical polymerization initiator can be used but it is preferred to use a is compound selected from the group consisting of 2,2xe2x80x2-azobisisobutyronitrile, acetylperoxide, laurylperoxide, and t-butylperoxide. The above polymerization reaction is preferably carried out at a temperature ranging from about 50 to about 90xc2x0 C. and each of the monomers has a mole fraction ranging from about 0. 01 to about 0.99.
An anti-reflective coating composition can comprise a polymer of Formula 1 and a polymer of Formula 2.
Further, an anti-reflective coating composition can comprise a polymer of Formula 1, a polymer of Formula 2 and an anthracene derivative as an additive. Illustrative, non-limiting examples of the anthracene derivatives (hereinafter, xe2x80x9canthracene derivative additivexe2x80x9d) is selected from the group consisting of anthracene, 9-anthracenemethanol, 9-anthracenecarbonitrile, 9-antracene carboxylic acid, ditranol, 1,2,10-anthracentriol, anthraflavonic acid, 9-anthraldehydeoxime, 9-anthraldehyde, 2-amino-7-methyl-5-oxo-5H-[1]benzo-pyrano[2,3-b]pyridine-3 -carbonitrile, 1-aminoanthraquinone, anthraquinone-2-carboxylic acid, 1,5-dihydroxyanthraquinone, anthrone, 9-anthryle trifluoro-methylketone, 9-alkylanthracene derivatives of the following Formula 7,9-carboxylanthracene derivatives of the following Formula 8,1-carboxylanthracene derivatives of the following Formula 9, and mixtures thereof. 
wherein, R1 to R5 are xe2x80x94H, xe2x80x94OH, xe2x80x94CH2OH or substituted or unsubstituted, straight or branched alkyl or alkoxyalkyl having 1 to 5 carbon atoms.
A preparation method of an organic anti-reflective coating comprises the steps of dissolving a polymer of Formula 1 and a compound of Formula 2 in an organic solvent, filtering the obtained solution alone or in combination with at least one anthracene derivative additive as aforementioned, coating the filtrate on a lower layer and hard-baking the coated layer. More particularly, any organic solvent can be used in the present preparation method but it is preferred to select the organic solvent from the group consisting of ethyl 3-ethoxypropionate, methyl 3-methoxypropionate, cyclohexanone, and propyleneglycolmethylether acetate. The aforementioned organic solvent is preferably used in an amount ranging from about 200 to about 5,000 wt. % based on the total weight of the anti-reflective coating resin used. The preferred temperature for hard-baking ranges from about 100 to about 300xc2x0.
A semiconductor device can be prepared from any of the aforementioned anti-reflective coating compositions discussed above.
Two monomers each having a chromophore of high absorbance (anthracenemethyliminealkylacrylate monomer and anthracenemethylmethacrylate monomer) was first synthesized to enable for a polymer made therefrom to show a high absorbance at the wavelength of 248 nm. The polymer made from these two monomers is referred to as a primary polymer (the compound of Formula 1). Because one of these two monomers having chromophore is weakly basic, it is believed that any undercutting due to an unbalanced acidity after finishing the coating is prevented. Further, in order to allow improved properties to a produced organic anti-reflective coating, such as good molding property, air-tightness, and dissolution resistance, a secondary polymer (the compound of Formula 2) capable of forming a cross linkage upon the reaction with an alcohol group in resin was also synthesized to cause a cross-linking reaction during a hard-baking step following a coating step. The secondary polymer mixed with the primary polymer can form a cross-linked product by a thermal reaction.
In particular, since the cross-linking agents used in the present invention being in the form of a polymer are designed to maximize the efficiency of the cross-linking reaction, it is possible to freely adjust the k value of the anti-reflective coating by controlling the proportion of the primary polymer.
Further, the anti-reflective coating resin of the present invention has a good solubility in all of the hydrocarbon solvents while has a dissolution resistance in any of the solvents during a hard-baking step. In addition, no undercutting or footing is experienced in the fabrication process of patterns using the same. Especially, because the anti-reflective coating resin of the present invention is made from acrylate polymer, which enables higher etching speed relative to, that of the photosensitive film during etching process, the etching selectivity is improved.